Products intended for the purposes of this invention have been in use since the earliest production manufacture of automobile tires. Tire making is still essentially a hand operation with the tire built up in a general barrel shape, open at top and bottom, and the uncured or green tire coated on the outside with an anti-blemish lubricant coating and the inside area of contact between a rubber bladder and the interior of the tire casing interface needs be lubricated with an inside tire coating lubricant or dope. The latter compositions are here of specific interest.
Subsequent to drying of the inside and outside of the uncured green tire, it is bag molded in what are commonly referred to as Bag-O-Matic molds. A rubber bladder expanded by a hot fluid, either liquid or gas, pushes the tire carcass into the cavity of the metal tire mold. The interior tire lubricant composition, as here more fully developed, provides lubricity between the exterior surface of the rubber bladder and the interior mold-created side walls of the cured tire. Additionally the interior, or inside tire coating must also permit entrapped air to be released which accumulates in the interface as the final shape of the tire is determined by the mold contour. In addition the coating must permit ready and free release of the rubber bladder from the tire interior after cure. The interior tire coating can contribute materially to the tire molding costs if one or more of the components of the subject coating contribute to deterioration of the bladder, or have residual deposit of components interiorly of the tire which may influence the service life in use of the tire carcass after the molding operation. Lubricity created by the coating is particularly important to the end of centering the tire in the mold, as well as preventing flaws from developing in the side walls and tread of the body.
After the mold is closed, the pressure of the hot fluid within the rubber bladder creates internal pressure in the metal mold. The tire while in the mold is heated from both outside and inside. The green tire or uncured rubber initially softens, forcing the tread into the negative tread pattern of the mold.
In the manufacture of bias ply tires in particular, there is a higher than usual "turn down" ratio (side wall bending process step) than in manufacture of most other tire qualities. Lubrication between the exterior walls of the expanding rubber bladder and the interior of the tire is particularly critical. Preferably the inside lubricant coating remains on the interior surface of the tire to leave the bladder surface free of foreign matter on withdrawal of the cured tire from the mold. The technology is more fully reviewed in U.S. Pat. No. 2,937,406 where Toddy describes the tire molding process in more complete detail.
Historically, dry powders were dusted onto the interior surfaces of the "green" tire body before cure in the mold. Mica, talc and graphite were used to provide lubrication and release. Control of the surface coating was obviously difficult, if not impossible.
With the rapid development of silicone chemistry, silicones in hydrocarbon solvents were formulated with various other products including mica. Proportions were found to be relatively critical to overcome blemishes, buckeled bladders, kinked tire beads, trapped air, etc. Additionally health hazards to the operators including fire and toxicity to hydrocarbon chemicals were objectionable.
Silicone emulsions were later developed permitting introduction of water to replace, at least in part, undesirable volatile hydrocarbons. However, emulsions are subject to instability and require other additives to permit storage life without deterioration.
So far as is known, a water-reducible paste product devoid of silicones has not heretofor been successfully introduced. It has been general experience that lubricity has not been of the order equal to the silicones, thus tire manufacturers have been willing to meet the additional costs such limitations inherently introduced in inside tire lubricants.
It is the principal objective of this invention to provide a volatile hydrocarbon free coating composition whose only volatile component is required for application on the job and consists essentially of water.
It is a further objective to provide a silicone-free, water-reducible band ply interior lubricant which has the quality of lubricity which is substantially equivalent to the prior, more costly silicone-containing coatings.